PRODUCTION
Epoxy coating goes onto a tank to protect it against the weather. The sprayequipment, demonstrated by Bakélite, at the Paint Industries* Show, mixes resin and hardener only an instant before the mixture is atomized and sprayed
Epoxy Coating Methods Shown N e w dry and liquid coating techniques may e x p a n d use of e p o x y resins as protective coatings JL w o new techniques for getting epoxy coatings onto base materials came to light at the annual meeting of the Federation of Paint and Varnish Production Clubs coupled with the Paint Industries* Show in Cleveland. One is a dry method, the other uses liquids. Both stand a good chance of expanding the use of epoxy coatings. Harrv W. Howard of Shell Chemical
demonstrated the dry technique before the meeting of the federation. Normally, this type of epoxy coating is applied as a liquid containing about 25 to 30% solids, then baked. In the new approach, the coating is put on as a 1007c solid. First, the metal to b e coated is heated, in this particular case, to 400° F . The sample is then immersed in an air suspension of the
finely divided resin formulation. Soon afterward, the metal is withdrawn, covered with a fine deposit of resin. The metal is then baked. A big advantage of this approach is that It requires no solvent. It eliminates the handling problems» hazards, and costs involved in using a solvent. Furthermore, it's possible to build u p unusually thick films quicldy. For example, an 8- to 10-mil coating can rapidly be applied in a single step. If a conventional liquid system were used, this film thickness might require as many as seven separate coats» with half-hour bakes between each to drive out the solvent. The new method can readily produce films in the range of about 5 to 20 mils, Howard says. Satis* factory films thinner than this, however, are difficult to come by. The method is now beginning to be used in the automotive and electrical fields. Studies are under way to determine how effective it might be for coating parts of household appliances, such as stoves and washing machines. Although at present the method is mainly being considered for treating metals, it might also be used on glass, plastics, and other materials. • Other Resins· Actually, this technique has for some time been used in depositing coatings of nylon, polyethylene» polyvinyl chloride, and Teflon. Its use with epoxies, however, is new. The powdered resin demonstrated by Howard consisted of a combination of 75 S p o t t e s t devised by Electromet discriminates between 200 series a n d 3 0 0 series stainless steels without the need for chemical analysis or spectroscopy. T h e procedure, says Electromet, is to place two drops of nitric acid followed b y one drop of hydrochloric acid on the specimen to b e tested. After the reaction has subsided, add two drops of w a t e r and mix with a glass stirring rod. A d d a pinch of sodium bîsinuthàw arid mix with t h e rod. If all t h e sodium bism u t h a t e dissolves, add small portions until excess reagent is present. After 3 0 seconds to a minute, says the comj p a n y , 200 series steels will give a dark reddish-brown spot, 300 series steels a t a n spot.
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• Chrom-Lume process, developed by Service Hard-Chromium Co., is a m e t h o d to plate chromium directly to a l u m i n u m and its alloys without an int e r m e d i a t e coat of copper, nickel, or zincate, according to the company. T h e process, says George Hompesch, Service Hard-Chromium's president, eliminates the possibility of galvanic action and prevents undesirable elect r o h tic couples. • O x y g e n - c y l i n d e r l e a k s can b e det e c t e d by putting the sealed cylinder of l i q u i d oxygen inside a helium-filled Walloon" of polyethylene film. I n this m e t h o d , devised b y Linde, a mass spectrometer picks u p any oxygen leaks. L i n d e uses 4-mil Yisqueen polyethylene
film.
